Two-shaft gas turbine

ABSTRACT

A two-shaft gas turbine includes a high-pressure turbine having an annular gas-passage outlet, a low-pressure turbine having an annular gas-passage inlet, an annular intermediate duct that connects the gas-passage outlet to the gas-passage inlet, a bearing that supports a rotor of the high-pressure turbine and that is attached to a bearing case, and a plurality of struts that support the bearing case. The struts are arranged radially along the circumference of the bearing case so as to extend though the intermediate duct in a space between an outer peripheral surface of the bearing case and an inner peripheral surface of a casing wall that surrounds the intermediate duct. The intermediate duct has strut covers through which the struts extend and which function as first-stage stator blades for the low-pressure turbine.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a gas turbine including a plurality of shafts arranged on the same axis.

2. Description of the Related Art

A typical gas turbine (not shown) includes a compressor, a combustor, and a turbine. In the gas turbine, air is compressed by the compressor and is supplied to the combustor, where the compressed air is mixed with fuel that is separately supplied and the mixture of the compressed air and the fuel is combusted. Combustion gas is generated by combustion and is supplied to the turbine, where energy of the combustion gas is extracted. The energy exerts a rotational driving force for the compressor and a driving force for causing a generator (not shown) to generate electricity. After the rotational driving force is generated by the turbine, the combustion gas is exhausted through an exhaust diffuser.

FIG. 7 shows an example of a commonly known two-shaft gas turbine used as a jet-engine-derivative gas turbine. This gas turbine includes a high-pressure turbine 100 having an annular gas-passage outlet 101, a low-pressure turbine 102 having an annular gas-passage inlet 103, an annular intermediate duct 104 that connects the gas-passage outlet 101 to the gas-passage inlet 103, a journal bearing 105 that supports a rotor of the high-pressure turbine 100, and a plurality of struts 108 that support the journal bearing 105. The struts 108 are radially arranged along the circumference of the journal bearing 105 and extend though strut covers 107 that are integrated with the intermediate duct 104 in a space between an outer peripheral surface of the journal bearing 105 and an inner peripheral surface of a casing wall 106 that surrounds the intermediate duct 104.

The high-pressure turbine 100 functions as a gas generator that generates high-temperature, high-pressure combustion gas for driving the compressor (not shown) and the low-pressure turbine 102 functions as a power turbine that drives a load (not shown) of a generator or the like to collect energy. In FIG. 7, reference numerals 109 and 110 denote first-stage stator blades and first-stage rotor blades, respectively, of the low-pressure turbine 102.

In the above-described two-shaft gas turbine, the strut covers 107 for preventing the struts 108 from being heated by the high-temperature gas are disposed in the gas passage between the high-pressure turbine 100 and the low-pressure turbine 102. Therefore, the strut covers 107 and the first-stage stator blades 109, which are disposed along the gas flow for the first-stage rotor blades 110, cause aerodynamic loss in the gas passage.

In addition, since the strut covers 107 and the first-stage stator blades 109 are arranged in tandem, namely, along the direction of gas flow, the length of the gas passage is increased. Therefore, the length of the low-pressure turbine 102 along the rotor shaft is also increased, which leads to an increase in the size of the gas turbine.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide a two-shaft gas turbine that is small and provides improved performance, wherein strut covers and first-stage stator blades are effectively integrated to reduce pressure loss in a gas passage and the length of the gas passage.

In order to achieve the above-described object, a two-shaft gas turbine according to the present invention includes a high-pressure turbine having an annular gas-passage outlet, a low-pressure turbine having an annular gas-passage inlet, an annular intermediate duct that connects the gas-passage outlet to the gas-passage inlet, a bearing that supports a rotor of the high-pressure turbine and that is attached to a bearing case, and a plurality of struts that support the bearing case. The struts are arranged radially along the circumference of the bearing case extend though the intermediate duct in a space between an outer peripheral surface of the bearing case and an inner peripheral surface of a casing wall that surrounds the intermediate duct. The intermediate duct has strut covers through which the struts extend and which function as first-stage stator blades of the low-pressure turbine.

The intermediate duct may be divided into a plurality of segments along the circumference thereof, each segment having one of the strut covers, and the struts may be provided so as to extend through an arbitrary number of the strut covers.

The intermediate duct may be divided into twenty segments and the struts may be provided so as to extend through ten of the strut covers, the strut covers without the struts and the strut covers having the struts being arranged alternately.

Each strut cover has a wing-shaped cross section in which the width of a front section of the strut cover gradually increases downstream in the direction of gas flow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of the main portion of a two-shaft gas turbine according to an embodiment of the present invention;

FIG. 2A is a sectional view of an intermediate duct;

FIG. 2B is a perspective sectional view of the intermediate duct;

FIG. 3A is an exploded sectional view of the intermediate duct;

FIG. 3B is an exploded perspective sectional view of the intermediate duct;

FIG. 4A is an exploded sectional view of the intermediate duct in another state;

FIG. 4B is an exploded perspective sectional view of the intermediate duct in another state;

FIG. 5 is a schematic diagram showing the overall structure of the two-shaft gas turbine;

FIG. 6 is a sectional view of FIG. 1 taken along line VI-VI; and

FIG. 7 is a sectional view of the main part of a known two-shaft gas turbine.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A two-shaft gas turbine according to an embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

As shown in FIG. 5, a two-shaft gas turbine according to the present embodiment includes a compressor 10, a combustor 11, a high-pressure turbine 12 that functions as a gas generator, and a low-pressure turbine 13 that functions as a power turbine.

In this two-shaft gas turbine, air is compressed by the compressor 10 and is supplied to the combustor 11, where the compressed air is mixed with fuel that is separately supplied and the mixture of the compressed air and the fuel is combusted. Combustion gas is generated by combustion is supplied to the high-pressure turbine 12 and the low-pressure turbine 13. The high-pressure turbine 12 generates high-temperature, high-pressure combustion gas for driving the compressor 10 at, for example, 5,000 rpm and the low-pressure turbine 13 drives a generator 14 at, for example, 3,000 rpm to collect the energy of the combustion gas.

As shown in FIGS. 1, 2A, and 2B, the high-pressure turbine 12 and the low-pressure turbine. 13 have an annular gas-passage outlet 15 and an annular gas-passage inlet 16, respectively, which are connected to each other with an annular intermediate duct 17. A bearing 19 that supports a rotor 18 of the high-pressure turbine 12 is attached to a bearing case 20 that is supported by a plurality of struts 23. The struts 23 are arranged radially along the circumference of the bearing case 20 and extend through strut covers 22 that are integrated with the intermediate duct 17 in a space between an outer peripheral surface of the bearing case 20 and an inner peripheral surface of an intermediate casing wall 21 that surrounds the intermediate duct 17.

The high-pressure turbine 12 has a gas passage in which stator blades 25 are supported by an inner casing wall 24A so as to be arranged in two stages and rotor blades 26 are supported by the rotor 18 at a position between the two stages of stator blades 25. An outer casing wall 24B of the high-pressure turbine 12 is fixed to the intermediate casing wall 21 with bolts. The low-pressure turbine 13 has a gas passage in which stator blades 28 supported by an inner casing wall 27A and rotor blades 29 supported by a rotor (not shown) are alternately arranged in multiple stages. An outer casing wall 27B of the low-pressure turbine 13 is also fixed the intermediate casing wall 21 with bolts.

The struts 23 are fixed to the bearing case 20 and the intermediate casing wall 21 at the ends thereof with stud bolts 30, nuts 31, and locking bolts (not shown).

According to the present embodiment, the strut covers 22 of the intermediate duct 17 through which the struts 23 extend function as first-stage stator blades in the low-pressure turbine 13. Therefore, although first-stage stator blades are disposed in a gas-passage inlet of a low-pressure turbine in a known structure, the first-stage rotor blades 29 are directly provided instead in the present embodiment.

More specifically, the intermediate duct 17 is divided into, for example, twenty segments along the circumference thereof, each segment being integrated with a single strut cover 22. Among the strut covers 22, the struts 23 are provided so as to extend through, for example, ten strut covers 22. In other words, the struts 23 are disposed in every other strut covers 22.

Each segment of the intermediate duct 17 is supported by the bearing case 20 at the inner end thereof with attachment members 32 a and 32 b provided therebetween, and is supported by the intermediate casing wall 21 at the outer end thereof with supporting members 33 a and 33 b provided therebetween. In FIG. 1, the upstream retaining member 33 a in the direction of gas flow is indirectly supported by the intermediate casing 21 with a connecting member 34 disposed therebetween.

As shown in FIG. 6, each strut cover 22 has a wing-shaped cross section in which the width of a front section of the strut cover 22 gradually increases downstream in the direction of gas flow. Accordingly, the strut covers 22 allow the gas to smoothly flow along the surfaces thereof without generating a shock wave, thereby effectively providing a function as nozzle blades for the first-stage rotor blades 29 in the low-pressure turbine 13.

FIGS. 3A and 3B show the state in which the intermediate casing wall 21 is detached from the structure shown in FIGS. 2A and 2B, respectively. FIGS. 4A and 4B show the state in which the struts 23 are pulled out from the structure shown in FIGS. 3A and 3B, respectively. The procedure for assembling the two-shaft gas turbine or replacing the struts 23 and/or the segments of the intermediate duct 17 can be understood from FIGS. 4A and 4B.

As described above, according to the present embodiment, the strut covers 22 of the intermediate duct 17 serve the function as first-stage stator blades (nozzle blades) of the low-pressure turbine 13. Therefore, unlike the known structure, it is not necessary to provide first-stage stator blades (nozzle blades) in the gas-passage inlet 16 of the low-pressure turbine 13, and the rotor blades 29 can be directly arranged.

Therefore, the pressure loss in the gas passage between the high-pressure turbine 12 and the low-pressure turbine 13 and the length of the gas passage in the low-pressure turbine 13 can be reduced. Therefore, the turbine performance can be increased and the size can be reduced at the same time.

In addition, according to the present embodiment, the intermediate duct 17 is divided into a plurality of segments along the circumference thereof, each segment being integrated with a single strut cover 22. In addition, the struts 23 may be provided so as to extend therethrough an arbitrary number of the strut covers 22. Therefore, the number of struts 23 to be installed can be changed as necessary. In addition, the struts 23 and the segments of the intermediate duct 17 can be easily replaced.

The present invention is not limited to the above-described embodiment. The number of segments into which the intermediate duct 17 is divided, the number of struts 23 to be installed, the cross sectional shape of each strut cover 22, etc. may, of course, be variously modified within the scope of the present invention. 

1. A two-shaft gas turbine comprising: a high-pressure turbine having an annular gas-passage outlet; a low-pressure turbine having an annular gas-passage inlet; an annular intermediate duct that connects the gas-passage outlet to the gas-passage inlet; a bearing that supports a rotor of the high-pressure turbine and that is attached to a bearing case; and a plurality of struts that support the bearing case, the struts being arranged radially along the circumference of the bearing case and extending though the intermediate duct in a space between an outer peripheral surface of the bearing case and an inner peripheral surface of a casing wall that surrounds the intermediate duct, wherein the intermediate duct is divided into a plurality of segments along the circumference thereof, each of the segments integrated with a single strut cover and provided detachably from one another, the struts extend through an arbitrary number of the strut covers, and the intermediate duct has strut covers through which the struts extend and which function as first-stage stator blades of the low-pressure turbine.
 2. (canceled)
 3. The two-shaft gas turbine according to, claim 1 wherein the intermediate duct is divided into twenty segments and the struts are provided so as to extend through ten of the strut covers, the strut covers without the struts and the strut covers having the struts being arranged alternately.
 4. The two-shaft gas turbine according to claim 1, wherein each strut cover has a wing-shaped cross section in which the width of a front section of the strut cover gradually increases downstream in the direction of gas flow. 